Minimal Structured Control Flow
See also: Structured program theoremIn May 1966, Böhm and Jacopini published an article in Communications of the ACM which showed that any program with gotos could be transformed into a goto-free form involving only choice (IF THEN ELSE) and loops (WHILE condition DO xxx), possibly with duplicated code and/or the addition of Boolean variables (true/false flags). Later authors have shown that choice can be replaced by loops (and yet more Boolean variables).
The fact that such minimalism is possible does not necessarily mean that it is desirable; after all, computers theoretically only need one machine instruction (subtract one number from another and branch if the result is negative), but practical computers have dozens or even hundreds of machine instructions.
What Böhm and Jacopini's article showed was that all programs could be goto-free. Other research showed that control structures with one entry and one exit were much easier to understand than any other form, primarily because they could be used anywhere as a statement without disrupting the control flow. In other words, they were composable. (Later developments, such as non-strict programming languages - and more recently, composable software transactions - have continued this line of thought, making components of programs even more freely composable.)
Read more about this topic: Control Flow
Famous quotes containing the words minimal, structured, control and/or flow:
“For those parents from lower-class and minority communities ... [who] have had minimal experience in negotiating dominant, external institutions or have had negative and hostile contact with social service agencies, their initial approaches to the school are often overwhelming and difficult. Not only does the school feel like an alien environment with incomprehensible norms and structures, but the families often do not feel entitled to make demands or force disagreements.”
—Sara Lawrence Lightfoot (20th century)
“Just as the constant increase of entropy is the basic law of the universe, so it is the basic law of life to be ever more highly structured and to struggle against entropy.”
—Václav Havel (b. 1936)
“Just as men must give up economic control when their wives share the responsibility for the family’s financial well-being, women must give up exclusive parental control when their husbands assume more responsibility for child care.”
—Augustus Y. Napier (20th century)
“No care, no stop; so senseless of expense
That he will neither know how to maintain it
Nor cease his flow of riot, takes no account
How things go from him, nor resumes no care
Of what is to continue.”
—William Shakespeare (1564–1616)